1. Field of the Invention
An aspect of the present invention relates to a defect correction method for an EUV mask.
2. Description of the Related Art
At present, transmission-type photomasks are used as exposure masks in manufacture of semiconductor integrated circuits. With those photomasks, reduction exposure is performed using mainly ultraviolet light of 248 nm or 193 nm in wavelength. In many cases, the optical magnification of the reduction exposure is set at ¼. Such transmission-type photomask will continue to be used for manufacturing memory devices whose half pitch is longer than about 30 to 40 nm, in view of their physical properties and manufacturing costs.
On the other hand, to manufacture further-miniaturized devices, other methods are being studied. One method is an extreme ultraviolet (EUV) photo-exposure technology. Photomasks (hereinafter referred to as EUV masks) in the EUV photo-exposure technology are used in reflection-type projection optical systems and thus different in structure from the transmission-type photomasks. The optical magnification in the EUV photo-exposure technology will remain ¼, as with transmission-type photomasks. To manufacture EUV masks, a technique for manufacturing finer mask patterns than with transmission-type photomasks is required.
In a manufacturing process of the EUV masks, defects may be formed on a mask pattern. To correct the defects formed on the mask pattern, a correction apparatus using a focused ion beam (FIB) or an electron beam (EB) is used. The correction apparatus of focused ion beam (FIB) is insufficient in beam resolution. The correction apparatus of electron beam (EB) has a high resolution, but etching on individual correction portion takes long time. To increase the etching speed when using the correction apparatus of electron beam (EB), it is attempted to use a highly reactive gas. However, in this case, etching proceeds excessively to disable a highly accurate correction (refer to JP-2004-537758-T, for example).